1. Field of the Invention
The present invention relates to capacitors having adjustable capacitance, and printed wiring boards having the capacitors.
2. Description of the Related Art
Printed wiring boards are originally used for mechanically holding electronic components such as semiconductor devices, for feeding these electronic components, and for establishing electric interconnections between the electronic components. The printed wiring boards therefore comprise, for example, land, pad, and through-hole conductors for mechanically holding the electronic components; wiring pattern conductors, via-hole conductors, and through-hole conductors for feeding them and establishing electric interconnection of them; and dielectric layers for mechanically holding these land, pad, and through-hole conductors, via-hole conductors, and wiring pattern conductors.
Printed wiring boards embedded resistor, inductor and/or capacitor components therein have been proposed for increasing the functions of such printed wiring boards and/or for reducing the number of surface mount electronic components.
The surface mounted components in package substrates for use in current electronic devices, however, must have performance with high precision as in individual components. For example, package substrates to be developed by the present inventors require a capacitance precision of the capacitor within about ±5%. The term “package substrate” used herein means a printed wiring board on which one or more electronic components were mounted.
The present inventors have found the following patent documents in this field: Japanese Patent Laid-open Publication No. 10-303062, entitled “Trimmable Capacitor” published on Nov. 13, 1998; and Japanese Patent Laid-open Publication No. 2000-340454, entitled “Method and Apparatus for Adjusting Capacitance” published on Dec. 8, 2000.
Japanese Patent Laid-open Publication No. 10-303062 discloses a method of adjusting the capacitance of a capacitor by constituting trimmable electrodes from an electroconductive material and a dielectric material that can have electroconductivity upon heating; imparting electroconductivity to part of the dielectric material by laser irradiation to thereby increase the electrode area; and trimming part of the electroconductive material to thereby reduce the electrode area.
Japanese Patent Laid-open Publication No. 2000-340454 discloses a method of adjusting the capacitance of a capacitor including a substrate and a pair of electrodes arranged on or above the substrate so as to face each other, in which the capacitance is adjusted by applying laser beams to one of the electrodes to form a trimming region having a predetermined area and a predetermined shape.